NateD26 wrote:I think it's the adverb πρότερον which modifies τῶν μέντοι βασιλέων with a repetition of the article.
The construction is article noun article modifier (adj./adv./pron./prep. phrase/etc.).
I have just reread what Taylor says on sandwich forms. The inner part of the sandwich (ie πρότερον in this case) specifies which of of the outer part is being talked about. He was a little laconic but with your pointer it all makes sense.
(I'm not sure what gave me the idea there must be grammatical agreement between the inner and outer part.)